The present invention generally relates to a combination starter-protector device for starting a dynamoelectric motor and also for protecting the windings thereof in the event of the occurrence of a current overload condition and, more particularly, to the combination starter-protector device of a type utilizing a positive temperature coefficient (PTC) thermistor, which device is adapted to be directly mounted to the dynamoelectric motor.
In existing single phase induction motors, such as condensor start induction motors and split phase type motors, a PTC thermistor has come to be used as a switching element for energizing the start winding of the motor and disassociating the start winding from the run or main windings of the motor when the motor attains its running speed. A typical combination starter-protector device now commercially utilized will now be described with particular referrence to FIG. 1 of the accompanying drawings.
As shown in FIG. 1, the single phase induction motor Mo of split phase type has three terminals 1, 2 and 3 and includes a run or main winding Lo connected between the terminals 1 and 2 and a start winding L.sub.1 connected between the terminals 1 and 3. The terminal 1 is adapted to be in turn connected to a source G of A.C. current through an overload relay 6 comprised of a heater 5 and a bimetallic thermostat 4, whereas the terminal 2 is adapted to be connected to the A.C. current source G through an on-off main switch SW. A PTC thermistor 7 is connected between the terminal 3 and the switch SW such that, when the switch SW is turned on, the PTC thermistor 7 is heated by the current flowing therethrough accompanied by a corresponding increase of the resistance thereof in response to the flow of such current. At the time when or after the resistance of the PTC thermistor 7 has attained a predetermined value great enough to permit the start winding L.sub.1 to effect a higher starting torque of the motor Mo during the start-up period thereof, the PTC thermistor 7 is disassociated from circuit relation with the run winding Lo, that is, substantially disconnected from the power source G, thereby minimizing a loss of electrical power which would otherwise be consumed by the start winding L.sub.1.
In the case of a conventional hermetic motor system, such as shown in FIG. 2 of the accompanying drawings, utilizing the single phase induction motor Mo of split phase type and utilizing the starter circuit shown in FIG. 1, the compressor motor is hermetically sealed within a compressor jacket or housing 8. In this system, the starter device 9 utilizing the PTC thermistor 7 is mounted on a chassis 10 of a housing 10a separate from the compressor jacket 8 whereas the motor terminals (glass terminals) 1, 2 and 3 are rigidly carried by the compressor jacket 8.
However, where the starter-protector device 9 is installed separately from the compressor jacket 8 in the manner as shown in FIG. 2, the following disadvantages and inconveniences have been found:
(1) A space for installation of the device 9 as well as a device housing 10a are required.
(2) A wiring is required between the device 9 and the motor terminals 1 to 3 and, therefore, a cumbersome and time-consuming work is required.
(3) In order for the device 9 to be substituted for the existing starter-protector device in which an electromagnetic relay assembly is utilized, the device 9 must be directly mounted to the compressor jacket 8.
(4) Since the PTC thermistor 7 in the device 9 constantly generates heat energies of a predetermined temperature, the heat energies tend to be dissipated to the outside through terminal elements 9a and 9b electrically connected to and supporting the PTC thermistor 7. This is particularly true where the terminal elements 9a and 9b, each partly exposed to the outside of the device housing 10a for external electrical connection, are made of copper alloy. The result is that the device 9 tends to consume a relatively large amount of the electrical power.
In addition to these disadvantages and inconveniences described above, there has been found such additional disadvantages that, since the overload relay 6 and the device 9 are spaced a distance from each other without being thermally coupled, the recovery time of the PTC thermistor is prolonged, and that, since the recovery time of the overload relay 6 is of a small value, the recovery time can not be balanced.
Examples of the prior art combination starter-protector device discussed above are disclosed in, for example. U.S. Pat. Nos. 4,037,316, patented July 26, 1977, and 4,042,860 patented Aug. 16, 1977.